This invention relates to a process for inspecting an electrode plate to be inspected (referred to hereinafter merely as an electrode plate), and more particularly to a process for inspecting the electrical connection state of electrodes of an electrode plate such as a printed wiring board having many electrodes or the like.
In general, many electrodes are formed on a printed circuit board, and in the case of such a printed wiring board, it is necessary to inspect whether the many electrodes are in the desired electrical connection state or in the desired insulation state in a stage before various functional parts are fabricated on the printed wiring board. For this inspection, it is necessary to achieve electric connection between an electrode plate such as a printed wiring board or the like and an inspection electrode plate having arranged thereon inspection electrodes corresponding to the electrodes to be inspected of the electrode plate by arranging the inspection electrode plate and the electrode plate so that the two lie one on the other.
For the above-mentioned purpose, an alignment between the electrode plate and the inspection electrode plate has heretofore been achieved by, for example, a means for fitting the alignment pins provided on the inspection electrode plate into the corresponding pin holes of the electrode plate, or other so-called mechanical alignment means.
In recent years, however, the parts packing density of printed wiring board has been increased and the density of pattern of printed wiring board has become higher. As a result, it is important to make the electrodes of the electrode plate smaller and the connection lines of the printed wiring board finer and arrange them in a higher density. However, when an alignment between such an electrode plate and an inspection electrode plate is only effected by a mechanical alignment means, merely a rough alignment state is obtained and it is impossible to sufficiently achieve the electrical connection of all inspection electrode pairs each consisting of an electrode to be inspected and an inspection electrode corresponding thereto.
The reasons therefor are that even when the electrodes to be inspected of the electrode plate and the inspection electrodes of the inspection electrode plate have basically the corresponding patterns, it follows that the electrodes to be inspected of the electrode plate are actually located in positions deviated, though slightly, from the design positions owing to a fine error caused in the production of the electrode plate or an error due to the deformation of the electrode plate per se. Also, there are similar situations in the inspection electrodes of the inspection electrode plate. Moreover, in the case of using alignment pins, a so-called play is required between the alignment pin and the corresponding pin hole and this becomes one of the causes of position deviation in the inspection electrode pair.
Under such circumstances, it is necessary to make a rough alignment between the electrode plate and the inspection electrode plate by, for example, a mechanical alignment means and then make a fine alignment to achieve precise position adjustment of the electrodes to be inspected of the electrode plate and the inspection electrodes of the inspection electrode plate.
For achieving such a fine alignment, a method has heretofore been known which comprises forming an appropriate alignment mark on an electrode plate in a specific position relation to the electrodes to be inspected; forming a control alignment mark on the inspection electrode plate in the same specific relation to the inspection electrodes as on the electrode plate; fixing the electrode plate onto a movable stage capable of moving in the lengthwise or crosswise direction or about the rotating axis; detecting the positions of the two alignment marks by an appropriate detection means; slightly moving the electrode plate relatively to the inspection electrode plate via the movable stage so as to remove the position deviation detected to thereby obtain a state in which the two alignment marks coincide in position with each other.
According to such a fine alignment means, however, it is impossible to completely remove the errors in position or shape of the alignment marks caused in the formation of the marks per se on the electrode plate and the inspection electrode plate, and errors appear to some extent in the detection of whether the two alignment marks coincide with each other. Therefore, a very complicated operation is required until the objective fine alignment has been sufficiently achieved, and even when a state in which the alignment marks coincide completely with each other has been obtained there is still a fear that there may be a case where the desired electrical connection state is not achieved in some actual inspection electrode pairs.
Also, in order to detect alignment marks on the electrode plate and the inspection electrode plate, it is necessary to provide, for example, an alignment mark-observing camera or other alignment mark detecting means. Moreover, such an alignment mark detecting means must be arranged above the alignment mark and in a direction vertical to the electrode plate, and, as a matter of course, the inspection electrode plate must be arranged so that the surface of the electrode plate is covered therewith. Hence, the alignment mark detecting means and the inspection electrode plate must be provided at the same place, which makes it very difficult to place them in adequate positions.
As described above, all of the conventional fine alignment methods aim at alignment between the electrodes of the electrode plate and the inspection electrodes of the inspection electrode plate; nevertheless it is not possible to exactly detect the position deviation state actually caused between the electrode plate and the inspection electrode plate because each of the methods uses an indirect deviation detecting means placed in a specific position relation to the electrode plate and the inspection electrode plate.
Also, as the result mentioned above, it is difficult to conduct an accurate fine alignment operation, and a long time and a complicated working are required until a state in which the position deviation has been removed and the desired alignment has been achieved is obtained. After all, it is impossible to achieve the desired inspection of an electrode plate with a high reliability in a high efficiency.